There is a lack of certified reference materials with an organic matrix for which metal isotope ratios have been certified. Here, we have determined the iron, copper and zinc stable isotopic compositions for six reference materials of biological origin with diverse matrices, i.e. BCR-380R (whole milk), BCR-383 (beans), ERM-CE464 (tuna fish), SRM-1577c (bovine liver), DORM-4 (fish protein) and TORT-3 (lobster hepatopancreas) in three different labs. The concentrations for six major and fifteen trace elements, spanning almost four orders of magnitude, were also measured and the results obtained show an excellent agreement with certified values, demonstrating that the dissolution step was quantitative for all the standards. By taking literature data into account, 39 possible pair-wise comparisons of mean iron, copper and zinc isotopic values (d values) could be made. Results of Tukey multiple comparisons of means yielded 11 significantly pairs. Most of these differences are of the same order of magnitude as the estimated mean expanded uncertainties (U , k = 2) (± 0.10 ‰, ± 0.05 ‰, and ± 0.05 ‰ for the δ 56 Fe, δ 65 Cu and δ 66 Zn values, respectively). The present inter-comparisons study finally proposes nineteen new isotopic compositions consensus values for six reference materials of biological origin.